Stacked interconnect structure and method of making the same

ABSTRACT

A method is provided of forming an interconnect structure. The method comprises forming a first dielectric layer overlying a first conductive layer, etching a trench opening in the first dielectric layer, depositing a sacrificial material layer in the trench opening, and forming a second conductive layer overlying the sacrificial layer. The method also comprises forming a via to the sacrificial layer, and performing an etch to remove the sacrificial material layer through the via and leave a resultant air gap between the first conductive layer and the second conductive layer increasing the effective dielectric constant between the first and second conductive layers.

TECHNICAL FIELD

The present invention relates generally to electronics, and more particularly to a stacked interconnect structure and method of making the same.

BACKGROUND

Commercial silicon complementary metal oxide semiconductor (CMOS) technology nodes require aggressive techniques in order to addresss the demands of shrinking technology geometries. Of particular concern in this work is the RC time delay, whose value needs to be kept low in order to maintain signal integrity. Scaling technology nodes tend to increase RC values, though, as metal lines shrink and therefore push resistance, R, higher and thinning inter-metal dielectric layers tend to increase capacitance, C. To some extent, these affects are mitigated by improved materials, such as transition to lower dielectric-constant insulators. State-of-the-art materials can be porous such as silicon carbide hydroxide (SiCOH) and copper metal lines. However, next-generation material selections are unresolved and even the most aggressive material cannot supplant air at the material of choice for low capacitance.

Increasingly aggressive RC time delay targets for back end of line (BEOL) interconnects have forced low effective dielectric constant technologies to struggle to keep pace with the needs of smaller technology nodes. In particular, ultra-low k porous SiCOH provides a dielectric constant of 2.4. However, even this is insufficient to support upcoming technologies and so some attempts at air gap technology have been established. These air gaps help isolated metal lines from adjacent ones, lowering the effective permittivity. However, still further reduction in RC is needed to keep pace with the International Technology Roadmap for Semiconductors (ITRS) and track Moore's law. Conducting lines will actually increase resistance as they shrink in size particularly as less conductive liner layers begin to dominate the resistive losses as compared to the copper. This will further exacerbate the RC performance dilemma.

SUMMARY

In accordance with an example, a method is provided of forming an interconnect structure. The method comprises forming a first dielectric layer overlying a first conductive layer, etching a trench opening in the first dielectric layer, depositing a sacrificial material layer in the trench opening, and forming a second conductive layer overly the sacrificial layer. The method also comprises forming a via to the sacrificial material layer, and performing an etch to remove the sacrificial material layer through the via and leave a resultant air gap between the first conductive layer and the second conductive layer increasing the effective dielectric constant between the first and second conductive layers.

In accordance with another example, a method is provided of forming an interconnect structure. The method comprises forming a first dielectric layer overlying a first conductive layer, etching a trench opening in the first dielectric layer, depositing a sacrificial material layer in the trench opening, and forming a second conductive layer overlying the sacrificial layer. The method further comprises forming an etch stop layer over the second conductive layer, etching away portions of the etch stop layer and the second conductive layer to provide a second conductive portion that over the first conductive layer, an etch stop that overlies the second conductive portion, and forming a third dielectric layer overlying the etch stop layer and the sacrificial layer. An etch is performed to concurrently to form a first via to the sacrificial layer and a second via to the etch stop of the second conductive portion. An etch is also performed to remove the sacrificial material layer through the first via and leave a resultant air gap between the first conductive layer and the second conductive portion increasing the effective dielectric constant between the first conductive layer and the second conductive portion.

In accordance with one example, an interconnect structure is provided that comprises a first conductive layer, a second conductive layer, and a dielectric layer disposed between the first and second conductive layers and having an air gap in the dielectric layer that separates the first and second conductive layers and increases the effective dielectric constant between the first and second conductive layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of an example of a portion of an interconnect structure.

FIG. 2 illustrates a graph comparing metal line width versus dielectric constant results of the air gap of the present disclosure versus acceptable results of the international semiconductor technology roadmap for future technology nodes.

FIG. 3 illustrates a graph comparing metal line width versus RC time constant results of air gap of the present disclosure versus acceptable results of the international semiconductor technology roadmap for future technology nodes.

FIG. 4 illustrates a cross-sectional view of an interconnect structure in its early stages of fabrication, and undergoing an etch process to form a trench opening.

FIG. 5 illustrates the resultant structure of FIG. 4 undergoing a deposition process to deposit a sacrificial layer in the trench opening.

FIG. 6 illustrates the resultant structure of FIG. 5 after undergoing the deposition process to deposit the sacrificial layer in the trench opening.

FIG. 7 illustrates the resultant structure of FIG. 6 after undergoing a deposition process to deposit a second dielectric layer over the sacrificial layer.

FIG. 8 illustrates the structure of FIG. 7 after undergoing deposition processes to deposit a second conductive layer over the second dielectric layer and an etch stop layer over the second conductive layer.

FIG. 9 illustrates the structure of FIG. 8 undergoing an etch process to remove portions of the second dielectric layer and the etch stop layer.

FIG. 10 illustrates the structure of FIG. 9 after undergoing the etch process of FIG. 9 to remove portions of the second dielectric layer and the etch stop layer.

FIG. 11 illustrates the structure of FIG. 10 after deposition of a third dielectric layer over the structure of FIG. 10.

FIG. 12 illustrates the structure of FIG. 11 undergoing an etch process to form a first via and a second via.

FIG. 13 illustrates the structure of FIG. 12 after undergoing the etch process to form a first via and a second via.

FIG. 14 illustrates the structure of FIG. 13 undergoing an etch process to remove the sacrificial layer.

FIG. 15 illustrates the structure of FIG. 14 after undergoing an etch process to remove the sacrificial layer.

DETAILED DESCRIPTION

The present disclosure provides for a stacked conductive layer interconnect approach to lower the effective dielectric capacitance in between stacked metal line layers, reducing the capacitance and hence, the RC constant. This is accomplished through the replacement of at least portions of insulating layers, such as porous silicon carbide hydroxide (SiCOH) with air gaps. In one example, the present disclosure provides for a method of making a back end of line interconnect structure provided with air gap technology in between layers of the conductive line interconnect structure. In so doing, the effective permittivity is substantially reduced, enabling RC propagation delays exceeding the needs of the international semiconductor technology roadmap for future technology nodes. FIG. 2 illustrates a graph 40 comparing metal line width (nm) versus dielectric constant incorporating the air gap with the materials used in the International Technology Roadmap for Semiconductors—2011 Edition. FIG. 3 illustrates a graph 50 comparing metal line width (nm) versus RC delay (psec/nm) the air gap with the materials used in the International Technology Roadmap for Semiconductors—2011 Edition. This new structure lowers the effective dielectric constant for intermediate metal layers to 1.2. In turn this reduces the RC time constant by 40% to 50%. In addition, a method is shown to create the airgap structure with an efficient one-mask process.

FIG. 1 illustrates a cross-sectional view of an example of a portion of an interconnect structure 10. The interconnect structure 10 includes a first dielectric layer 14 overlying a conductive layer 12. The conductive layer 12 could overly a substrate or one or more other conductive layers (not shown), for example, separated by dielectric layers and/or air gaps between conductive layers. A second dielectric layer 16 overlies the first dielectric layer 14 and includes an air gap 18 that separates the first conductive layer 12 from a second conductive layer 22. A portion of a second dielectric layer 16 overlies the air gap 18 and a portion of the second dielectric layer 16 overlies the first dielectric layer 14. A first via 26 is connected to the air gap 18 through a third dielectric layer 18 that overlies the second dielectric layer 16 and the second conductive layer 22. Although FIG. 1 illustrates that the second conductive layer 22 appears to run generally perpendicular to the first conductive layer 12, both the first and second conductive layers 12 and 22, respectively, could run parallel or perpendicular relative to one another separated by the air gap 20.

The first via 26 was utilized to remove a sacrificial layer (e.g., polysilicon) that was deposited and removed to form the air gap 20, as will be further discussed regarding formation of the interconnect structure, and air gap. A second via 28 extends to the second conductive layer 22 to provide a mechanism for connecting other layers and/or devices to the second conductive layer 22. The first and second vias 26 and 28 are formed in a single mask step. However, as can be seen from FIG. 1, the first via 26 extends much further than the second via 28, so a remaining portion of an etch stop layer 24 is illustrated overlying two opposite portions of the second conductive layer 22 that was utilized to protect the second conductive layer 22 from further etching during the formation of the second via 28 and the first via 26 down to the sacrificial layer (not shown).

Turning now to FIGS. 4-15, an example fabrication is discussed in connection with formation of the example of an interconnect structure. FIG. 4 illustrates a cross-sectional view of an interconnect structure in its early stages of fabrication. The interconnect structure includes a first dielectric layer 62 deposited over a first conductive layer 60. The first conductive layer 60 can be formed of any of a variety of conductive materials, such as copper, gold, titanium, aluminum, molybdenum, platinum, silver, or a combination of these or other conductive materials. Any suitable technique for depositing the conductive layer 60 can be employed such as sputtering, electroplating, metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE) or other suitable deposition techniques. The first dielectric layer 62 could be a dielectric layer that is selected to have a generally high dielectric constant, such as porous SiCOH. However, other dielectric layers with generally high dielectric constants could be employed.

A patterned photoresist material layer 64 is applied to cover the structure and is then patterned and developed to expose an open region 66 in the photoresist material layer 64 in accordance with an opening pattern. The photoresist material layer 64 can have a thickness that varies in correspondence with the wavelength of radiation used to pattern the photoresist material layer 64. FIG. 4 also illustrates performing of an etch process 200 to remove portions of the first dielectric layer 62 to extend the opening and form a trench opening 68 (FIG. 5) in the first dielectric layer 62. The resultant structure is illustrated in FIG. 5.

FIG. 5 illustrates the resultant structure undergoing a deposition process 210 to deposit a sacrificial layer 70 (FIG. 6) in the trench opening 68. The sacrificial layer 70 is formed of a material that can be etched away by an etchant at a substantially faster rate than the dielectric material layers employed to form the interconnect structure. In one example, the sacrificial layer 70 is formed from polysilicon. This can be selectively removed employing a vapor phase etch of Xenon Fluoride (XeF₂). However, other sacrificial materials could be employed. The photoresist material layer 64 is then stripped. The sacrificial layer 70 can be polished via chemical mechanical polishing (CMP) flush with the top surface of the first dielectric layer 62 to provide the resultant structure of FIG. 6. FIG. 6 also illustrates the structure undergoing a deposition process 220 to deposit a second dielectric layer 72 over the sacrificial layer 70. The resultant structure is illustrated in FIG. 7.

FIG. 8 illustrates the structure of FIG. 7 after undergoing the first deposition process 72 to deposit a second conductive layer 74 over the second dielectric layer 72, and a second deposition process to deposit an etch stop layer 76 over the second conductive layer 74. The second conductive layer 74 can be formed of any of a variety of conductive materials, such as copper, gold, titanium, molybdenum, platinum, silver, or a combination of these or other conductive materials. The etch stop layer 76 can be formed of a variety of materials, such as Titanium Nitride (TiN) or other types of etch stop materials.

Any suitable technique for depositing each layer can be employed such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), Low Pressure Chemical Vapor Deposition (LPCVD), Plasma Enhanced Chemical Vapor Deposition (PECVD), High Density Chemical Plasma Vapor Deposition (HDPCVD), Atomic Layer Deposition (ALD), physical vapor deposition or high density plasma chemical vapor deposition (HDPCVD) techniques, spin on techniques, or other suitable deposition techniques.

Next, as represented in FIG. 9, a photoresist material layer 78 is applied to cover the structure and is then patterned to protect regions where a second conductive portion 80 is to be formed from the second conductive layer 74. The second conductive portion 80 can be a conductive line, a traversing conductive layer or simply a modified layer or other conductive structure of the second conductive portion 80. The photoresist material layer 78 can have a thickness that varies in correspondence with the wavelength of radiation used to pattern the photoresist material layer 78. The photoresist material layer 78 may be formed over the substrate via spin-coating or spin casting deposition techniques, selectively irradiated and developed. FIG. 9 also illustrates performing of an etch process 230 on the etch stop layer 76 and the second conductive layer 74 to provide a portion of a conductive layer or a second conductive portion 80 and a portion of an etch stop layer or an etch stop 82 overlying the second conductive portion 80. The etch process 230 could be a single etch process or multiple etch process. The resultant structure is illustrated in FIG. 10.

FIG. 11 illustrates the structure of FIG. 10 after undergoing a deposition process to deposit a third dielectric layer 84 over the etch stop 82 and second conductive portion 80. Next, as represented in FIG. 12, a photoresist material layer 86 is applied to cover the structure and is then patterned to expose open regions 88 and 90 in the photoresist material layer 86. The photoresist material layer 86 can have a thickness that varies in correspondence with the wavelength of radiation used to pattern the photoresist material layer 86. The photoresist material layer 86 may be formed over the structure via spin-coating or spin casting deposition techniques, selectively irradiated and developed to form the openings 88 and 90.

FIG. 12 also illustrates performing of an etch process 240 (e.g., anisotropic reactive ion etching (RIE)) to form a first via 92 down to the sacrificial layer 70, and a second via 94 that stops on the etch stop layer 82. The etch process 240 can be a dry etch that employs an etchant which selectively etches the material of the second and third dielectric layers 72 and 84 at a faster rate than the underlying sacrificial layer 70, and the overlying etch mask formed from the photoresist material layer 86. The etch process 240 can also be an etch that employs and etchant that selectively etches the third dielectric layer 84 but stops on the etch stop 82 to protect the second conductive portion 80. For example, the structure may be anisotropically etched with a plasma gas(es), herein carbon tetrafloride (CF₄) containing fluorine ions, in a commercially available etcher, such as a parallel plate RIE apparatus or, alternatively, an electron cyclotron resonance (ECR) plasma reactor to replicate the mask pattern of the etch mask to thereby form the first and second vias 92 and 94, respectively. The resultant structure is illustrated in FIG. 13.

FIG. 14 illustrates the structure of FIG. 13 undergoing an etch process 250 on the sacrificial layer 70 to remove portions of the sacrificial layer 70 (FIG. 15) overlying the first dielectric layer 62, and underlying the second dielectric layer 72 to form an air gap 96 between the first conductive layer 60 and the second conductive portion 80 to increase the dielectric constant between the first conductive layer 60 and the second conductive portion 80. The etching process 250 can be a dry etch process. In one example, the dry etch is a vapor phase etch technique that employs a Xenon Fluoride (XF₂) gas. FIG. 15 also illustrates performing of an etch process 260 (e.g., anisotropic reactive ion etching (RIE)) to remove a portion of the etch stop 82 overlying the second conductive portion 80 in the second via 94, thereby exposing a top layer of the second conductive portion 80 to provide a mechanism for connecting other layers and/or devices to the second conductive portion 80. The photoresist material layer 86 is then stripped to leave a resultant structure that is similar to the structure shown in FIG. 1.

What have been described above are examples of the invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the invention are possible. Accordingly, the invention is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims. 

1. A method of forming an interconnect structure, the method comprising: forming a first dielectric layer overlying a first conductive layer; etching a trench opening in the first dielectric layer; depositing a sacrificial material layer in the trench opening; forming a second conductive layer overlying the sacrificial layer; forming a via to the sacrificial layer; and performing an etch to remove the sacrificial material layer through the via and leave a resultant air gap between the first conductive layer and the second conductive layer decreasing the effective dielectric constant between the first and second conductive layers, and decreasing the RC time constant of the interconnect structure.
 2. The method of claim 1, further comprising forming a second dielectric layer over the sacrificial layer prior to forming the second conductive layer.
 3. The method of claim 1, further comprising: forming an etch stop layer over the second conductive layer; etching away portions of the etch stop layer and the second conductive layer to provide a second conductive portion over the first conductive layer, and an etch stop that overlies the second conductive portion; and forming a second dielectric layer overlying the etch stop layer and the sacrificial layer.
 4. The method of claim 3, further comprising forming an intermediate layer in between the sacrificial layer and the second dielectric layer.
 5. The method of claim 4, wherein the performing an etch to remove the sacrificial material layer through the via further comprises concurrently etching a second via to the second conductive portion stopping on the etch stop layer.
 6. The method of claim 5, further comprising performing an etch to remove the etch stop down to the second conductive layer.
 7. The method of claim 3, wherein the etch stop layer is titanium nitride (TiN).
 8. The method of claim 1, further comprising forming a third dielectric layer over the second dielectric layer and the second conductive layer.
 9. The method of claim 1, wherein the first dielectric layer is porous silicon carbide hydroxide (SiCOH).
 10. The method of claim 1, wherein the performing an etch to remove the sacrificial material layer comprises performing a vapor phase etch.
 11. The method of claim 1, wherein the sacrificial layer is polysilicon and the etch employs a Xenon Fluoride (XeF₂) gas.
 12. A method of forming an interconnect structure, the method comprising: forming a first dielectric layer overlying a first conductive layer; etching a trench opening in the first dielectric layer; depositing a sacrificial material layer in the trench opening; forming a second conductive layer overlying the sacrificial layer; forming an etch stop layer over the second conductive layer; etching away portions of the etch stop layer and the second conductive layer to provide a second conductive portion over the first conductive layer, and an etch stop that overlies the second conductive portion; forming a third dielectric layer overlying the etch stop layer and the sacrificial layer; performing an etch to concurrently form a first via to the sacrificial layer and a second via to the etch stop of the second conductive portion; and performing an etch to remove the sacrificial material layer through the first via and leave a resultant air gap between the first conductive layer and the second conductive portion decreasing the effective dielectric constant between the first conductive layer and the second conductive portion.
 13. The method of claim 12, further comprising performing an etch to remove the etch stop down to the second conductive layer.
 14. The method of claim 12, wherein the etch stop layer is titanium nitride (TiN).
 15. The method of claim 12, wherein each of the first dielectric layer, a second dielectric layer and the third dielectric layer are porous silicon carbide hydroxide (SiCOH).
 16. An interconnect structure comprising: a first conductive layer; a second conductive layer; and a dielectric layer disposed between the first and second conductive layers and having an air gap in the dielectric layer that separates the first and second conductive layers and decreases the effective dielectric constant between the first and second conductive layers and decreases the RC time constant of the interconnect structure.
 17. The structure of claim 16, wherein the dielectric layer is porous silicon carbide hydroxide (SiCOH).
 18. The structure of claim 16, wherein the second dielectric layer traverses the first conductive layer.
 19. The structure of claim 16, further comprising a first via that extends down to the air gap and a second via that extends down to the second conductive layer through a third dielectric layer.
 20. The structure of claim 19, further comprising an intermediate dielectric layer between the air gap and the second conductive line. 